The present invention relates to cryptographic systems and more particularly to an electronic cryptographic encoder-decoder primarily for use with commercial telephone and telegraph networks.
The increased use of telegraphic and data communications to handle financial and other sensitive data on the commercial telephone and telegraph networks has increased the risk of unauthorized disclosures. The cause is two-fold; first, just the increased traffic and, secondly, the increased exposure of this information to intelligent eavesdroppers. While many cryptographic devices have been developed for both the government and the commercial markets, the cost of such devices has been rather large.
Several years ago a simple pocket or hand-held cryptographic encoder-decoder was developed and is still in use. FIGS. 1 and 2 of the drawing illustrate this hand-held cryptographic encoder-decoder. As shown in FIG. 1, the device includes a relatively small, thin body portion 1 containing therein a plurality of slots 2, in this instant five, with the body portion 1 being capable of receiving sliders 3 registered with slots 2 and containing thereon various sequences of the characters or letters of the alphabet together with a numerical value which, when properly selected, will provide the code-of-the-day or -the-message. The code-of-the-day or -the-message 26589 is shown in the windows 4 in side A of body 1. Adjacent each of the slots 2 are letters in the normal alphabetical sequence. To encrypt a message, each letter of a word is found on body 1 adjacent one of the slots 2. A ball-point pen or other similar device is inserted into the round holes 5 of the sliders 3 and the encrypted letters will appear in windows 4 as shown in FIG. 2, wherein the word encrypted was "model." To encrypt the next word or the next five letters, the user goes to side B or the backside of the device in FIGS. 1 and 2, then back to side A and so forth alternately. The side B of the hand-held encryption device of FIGS. 1 and 2 is identical to that shown with the exception that the alphabetical sequence on the sliders 3 is the inverse of that shown. When decrypting an encrypted message by this hand-held device, the code-of-the-day is set up in windows 4 on side A and the message is decrypted by starting on side B first, then working to side A then back to side B, which process continues alternately between the two sides.
At the time the device of FIGS. 1 and 2 was developed, it was not found economical to produce an electrical encoder-decoder equivalent to the hand-held device of FIGS. 1 and 2 that would be convenient to use at a central location.